Câu 5:

a: Xét ΔAHB vuông tại H và ΔAHC vuông tại H có

AB=AC

AH chung

Do đó: ΔAHB=ΔAHC

b: Xét ΔDIH vuông tại I và ΔDIC vuông tại I có

DI chung

IH=IC

Do đó: ΔDIH=ΔDIC

=>DH=DC
=>ΔDHC cân tại D

c: Ta có: ΔAHB=ΔAHC

=>HB=HC

=>H là trung điểm của BC

Ta có: \(\hat{DHC}+\hat{DHA}=\hat{AHC}=90^0\)

\(\hat{DCH}+\hat{DAH}=90^0\) (ΔAHC vuông tại H)

mà \(\hat{DHC}=\hat{DCH}\)

nên \(\hat{DHA}=\hat{DAH}\)

=>DH=DA

mà DH=DC

nên DA=DC

=>D là trung điểm của AC

Xét ΔABC có

BD,AH là các đường trung tuyến

BD cắt AH tại G

Do đó: G là trọng tâm của ΔABC

Xét ΔABC có

G là trọng tâm

M là trung điểm của AB

Do đó: C,G,M thẳng hàng

=>CG=2GM

Xét ΔGHB vuông tại H và ΔGHC vuông tại H có

GH chung

HB=HC

Do đó: ΔGHB=ΔGHC

=>GB=GC

=>GB=2GM

=>\(GM=\frac12GB\)

Tham khảo cách thêm các cụm C-V làm phụ ngữ cho các danh từ trong những câu đã cho như sau: a. Bài báo cáo anh viết rất hay. b. Cuốn sách anh cho mượn có nhiều tranh minh họa

\(2^{10}:64\cdot16\)

\(=2^{10}:2^6\cdot2^4\)

\(=2^{10-6+4}\)

\(=2^8\)

\(2^{10}.64.16\\ =2^{10}.2^6.2^4\\ =2^{10+6+4}=2^{20}\)

refer

They/ play/ tennis/ 10.30 yesterday morning.

→ They were playing tennis at 10.30 yesterday morning .
Ann/ do/ homework/ 5 o’clock this afternoon.

→ Ann was doing homework at 5 o'clock this afternoon.
My father/ wash/ car/ from/ five to six.

→ My father was washing a/the/his car from five to six.
This time last year/ we/ live/ France.

→ This time last year , we were living in France .
The students/ offer/ flowers/ the visitors.

→ This students offered flowers to the visitors.
I/ cook/ dinner/ half an hour ago.

→ I was cooking dinner half an hour ago.
She/ work/ the studio/ that time.

→ She was working the studio at that time.
What/ you/ do/ from 3 to 6 yesterday afternoon?

→ What were you doing from 3 to 6 yesterday afternoon?

1 They were playing tennis at 10.30 yesterday morning

2 Ann was doing her homework at 5 o'clock this afternoon

3 My father was washing his car from five to six

4 This time last year we were living in France

5 The students were offering the flowers to the visitors

6 I was cooking dinner half an hour ago

7 She was working at the studio at that time

8 What were you doing from 3 to 6 yesterday afternoon?

Ta có: \(H=\frac{-7}{9}\cdot\frac{4}{11}+\frac{-7}{9}\cdot\frac{7}{11}+5\frac79\)

\(=-\frac79\left(\frac{4}{11}+\frac{7}{11}\right)+5+\frac79\)

\(=-\frac79+5+\frac79\)

=5

VIII

1. the

2. the

3. the